That I would agree with. But for what its worth, carbon build up is not all that easy and simple to get out. Yes, Seafoam would probably help, but where most of the carbon is going to be if not all of it is in the combustion chamber and for that you can run a good quality fuel injector, water/methanol injection (i.e. steam clean) or get it out on the highway from time to time and get it hot enough long enough to burn the stuff out of there.
But you are correct in that the two products work on two different areas of the engine.
